Method and Apparatus for Forming Cutting Blades

ABSTRACT

There is provided a method of forming cutting blades using selective laser melting comprising positioning a first part of an elongate strip with pre-formed teeth within a powder bed, forming coating layers layer-by-layer to create a cutting surface on each pre-formed tooth by repeatedly depositing a layer of powder on the powder bed and scanning a laser beam over the deposited powder to fuse powder to the pre-formed teeth.

CROSS-REFERENCE TO RELATED PATENT APPLICATION

This application is a continuation of U.S. application Ser. No.16/675,150, filed Nov. 5, 2019, claims the benefit of and priority toUnited Kingdom Application No. GB 1818678.3 filed on Nov. 16, 2018,which are incorporated herein by reference in their entireties.

FIELD OF THE INVENTION

This invention relates to a method and apparatus for forming cuttingblades using selective laser melting.

BACKGROUND TO THE INVENTION

Cutting blades are typically formed by depositing abrasive cuttingmaterial onto elongate strips or discs with pre-formed teeth. Generallythe teeth need to be ground or sharpened after the abrasive material hasbeen deposited. This increases the time needed for manufacture. Further,to ensure that the cutting surface adheres appropriately to the teeth,winding materials need to be selected carefully which furthercomplicates processing.

SUMMARY OF THE INVENTION

In accordance with a first aspect of the invention, there is provided amethod of forming cutting blades using selective laser meltingcomprising positioning a first part of an elongate strip with pre-formedteeth within a powder bed, forming coating layers layer-by-layer tocreate a cutting surface on each pre-formed tooth by repeatedlydepositing a layer of powder on the powder bed and scanning a laser beamover the deposited powder to fuse powder to the pre-formed teeth. Thisallows a cutting surface to be formed on each pre-formed tooth in amanner that avoids the need for grinding or sharpening of the cuttingsurface. Further, waste of the powder is avoided as excess powder isretained within the powder bed for re-use.

Preferably after creating the cutting surface, the method furthercomprises moving the elongate strip through the powder bed to present anadjoining part of the elongate strip with pre-formed teeth ready for theformation of coating layers.

The cutting surface may be substantially two-dimensional, such as isrequired for elongate saw blades or cutting discs. Alternatively thecutting surface can be three-dimensional. The use of selective lasermelting allows the customisation of the shape of the cutting surface asa preferred profile for the cutting surface can be programmed intosoftware controlling operation of the laser beam allowing customisationof the shape of the cutting surface.

The method may further comprise positioning multiple elongate stripswithin the powder bed. This improves overall throughput. Typically thestrips will be spaced-apart and parallel to each other.

The powder may preferably comprise super-hard particles in a metalmatrix. Super-hard particles may comprise, for example, Tungsten Carbidewith Cobalt, borides or Aluminium Oxide. The matrix may comprise Cobalt,or Chromium or Titanium or mixtures of these materials.

The elongate strip will typically be formed of metal such as steel.

Deposition may take place with a flow of inert gas over the powder bed.Alternatively the powder bed may be placed in a vacuum or within achamber filled with inert gas.

In accordance with another aspect of the invention, there is provided acutting blade formed in accordance with the method and its preferredsteps as described above.

In accordance with a further aspect of the invention, there is provideda cutting blade having a three-dimensional cutting surface formed inaccordance with the method and its preferred steps as described above.

In accordance with a yet further aspect of the invention, there isprovided apparatus for forming cutting blades using selective lasermelting, the apparatus comprising a laser and a powder bed, whereinfirst and second opposing walls of the powder bed are provided with atleast one pair of opposing slits with a sealing element located aroundeach slit so as to prevent loss of powder from the powder bed whilstallowing passage of a cutting blade through the slits.

A plurality of pairs of opposing slits may be provided so as to allowprocessing of a plurality of cutting blades at once, with each slitsealed against powder loss by a sealing element. One elongate sealingelement extending along the wall may be used to seal all slits alongthat wall or individual sealing elements may be used for individualslits.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described, by way of example, and withreference to the accompanying drawings in which:

FIG. 1 shows a schematic diagram of a processing apparatus for sawblades;

FIGS. 2(a) to (d) show schematic diagrams of processing undertaken bythe apparatus; and

FIG. 3 shows cross-sections of different three-dimensional saw toothprofiles.

DESCRIPTION

FIG. 1 shows a schematic diagram of apparatus 10 used for selectivelaser melting comprising a laser module 12 and powder dispenser 14 underthe control of processor or computer 16 and powder bed 20 includingapertured edge seals 22, 22′. Laser module 12 comprises a device forgenerating a laser combined with a galvanometer scanner 23 forming partof laser beam delivery system 25 moves the highly focussed laser beam 24across powder bed 20. Powder bed 20 is substantially rectangular withopposing edge walls 26, 27 formed with a plurality of vertical slits 28overlain by apertured edge seals 22 such that metal strips 30 requiringprocessing can be fed through powder bed 20 without powder beingreleased through slits 28. Typically powder bed 20 will have a width andlength of 200 mm due to the limited scanning area of laser module 12. Anadditional laser and scanner can be employed to increase the throughputor increase the powder bed size.

Strips 30 are elongate steel strips formed with pre-formed teeth 32 asseen in FIG. 2 . The pre-formed teeth 32 are shown as beingsubstantially rectangular in profile but other profiles can be adoptedif required. The processing sequence for strips 30 is shown in FIGS.2(a), (b), (c) and (d).

At the start of processing as in FIG. 2(a), a portion 34 of pre-formedstrip 30 is positioned within powder bed 20 and a thin layer 36 ofaround 0.05 to 0.10 mm of super-hard particles in a metal matrix,typically a sintered and agglomerated powder, is spread across the topsurface of the powder bed so as to overlie pre-formed teeth 32. Thesuper-hard particles can be a mixture of Tungsten Carbide and Cobalt,typically 80% Tungsten carbide and 20% Cobalt, or borides, or aluminiumoxide. The matrix can be Cobalt, or Chromium or Titanium or mixtures ofthese materials.

As shown in FIG. 2(b), galvanometer scanner 23 forming part of lasermodule 12 moves the highly focussed laser beam 24 across powder bed 20and fuses powder to each of pre-formed teeth 32 to form a first coatinglayer. A new layer of powder 38 is then spread across and over the fusedfirst coating layer, see FIG. 2(c), and the scanning of laser beam 24and fusing of powder repeated again. This is continued for successivecoating layers which are built layer-by-layer until the desired heightand profile of the cutting edge 39 is achieved. Portion 34 of coatedstrip then moves out of powder bed 20, see FIG. 2(d), with the nextadjoining section of strip fed into powder bed 20 for steps (a) to (d)to be repeated.

As shown in FIG. 1 , multiple strips 30 can be processed at the sametime, with the portion 34 of the elongate strips within the powder bedprocessed in one operation. When processing is complete, the strip movedalong by a distance equal to the width of the powder bed so as to thenprocess the next adjoining region of strip. Continuous automatedprocessing is possible on an unmanned basis.

Processor 16 can be programmed with different profiles for the cuttingsurface and these may be substantially two-dimensional representing anextension of the pre-formed tooth 32 or three-dimensional to createcustomised three-dimensional shapes on top of the pre-formed tooth. FIG.3 shows some cross-sections of three-dimensional cutting edges of sawtooth that can be achieved, 40 being an inverted frusto-conical cone ontop of the pre-formed tooth, 42 having a pentagonal cross-section, 44being a bifurcated shape with a substantially V-shaped cross-section and46 representing a stack of three frusto-conical sections.

The ability to customise the configuration of the cutting surface formedfrom the build up of coating layers allows complex cutting shapes to becreated depending on a customer's requirements, with software withinprocessor 16 being configurable to modify the coating layers to achievethe desired profile.

Using the selective melting process means that the cutting surface canbe formed as required into a final cutting profile ready to use, withoutthe need for grinding or sharpening. This allows super-hard materials tobe deposited as the coating layers to create the cutting surface as noto minimal grinding or sharpening is required to create the cuttingsurface, rather the final cutting surface, ready to use, is formeddirectly during the SLM process. Sometimes some grinding and sharpeningmay still be needed but this will be minimal and much less than isrequired for existing methods of manufacture of cutting blades.

Using a powder bed ensures that all powder is used in the manufacturingprocess without wastage of powder, which can be very expensive. Theranges of powder that can be used are extended as the SLM process cancope with much harder materials so much harder cutting edges can beprovided.

What is claimed is:
 1. A cutting blade, comprising: an elongate strip formed from a first material; a plurality of pre-formed teeth formed from the first material, the plurality of pre-formed teeth extending from the elongate strip; and at least one coating layer of a second material, the at least one coating layer comprising a first coating layer fused to the plurality of pre-formed teeth, the second material being harder than the first material; wherein the at least one coating layer defines a cutting edge of the cutting blade.
 2. The cutting blade of claim 1, wherein the first material is a steel.
 3. The cutting blade of claim 1, wherein each of the plurality of pre-formed teeth comprise a rectangular profile.
 4. The cutting blade of claim 1, wherein the at least one coating layer comprises a second coating layer fused to the first coating layer.
 5. The cutting blade of claim 1, wherein each of the at least one cutting layer has a thickness in a range from 0.05 mm to 0.10 mm.
 6. The cutting blade of claim 1, wherein the second material comprises a mixture of tungsten carbide and cobalt.
 7. The cutting blade of claim 6, wherein the mixture comprises 80% tungsten carbide and 20% cobalt.
 8. The cutting blade of claim 1, wherein the at least one coating layer comprises a substantially two-dimensional extension of the plurality of pre-formed teeth.
 9. The cutting blade of claim 1, wherein the at least one coating layer comprises a three-dimensional shape extending from the plurality of pre-formed teeth.
 10. The cutting blade of claim 9, wherein the three-dimensional shape comprises an inverted frusto-conical cone.
 11. The cutting blade of claim 9, wherein the three-dimensional shape comprises a pentagonal cross-section.
 12. The cutting blade of claim 9, wherein the three-dimensional shape comprises a bifurcated shape with a substantially V-shaped cross-section.
 13. The cutting blade of claim 9, wherein the three-dimensional shape comprises a stack of multiple frusto-conical sections.
 14. The cutting blade of claim 1, wherein the second material comprises particles of tungsten carbide, aluminum oxide, a boride, or combinations thereof and a matrix of cobalt, chromium, titanium, or mixtures thereof.
 15. The cutting blade of claim 1, wherein the elongate strip comprises a first edge extending along a length of the elongate strip and a second edge extending along a length of the elongate strip, wherein the first edge and the second edge are separated across a width of the elongate strip, and wherein the first edge defines the plurality of pre-formed teeth.
 16. An apparatus for forming cutting blades using selective laser melting, the apparatus comprising: a laser; and a powder bed; wherein first and second opposing walls of the powder bed are provided with at least one pair of opposing slits with a sealing element located around each slit so as to prevent loss of powder from the powder bed whilst allowing passage of a cutting blade through the slits.
 17. The apparatus for forming cutting blades according to claim 16, wherein a plurality of pairs of opposing slits are provided so as to allow processing of a plurality of cutting blades at once, with each slit sealed against powder loss by a sealing element.
 18. The apparatus for forming cutting blades according to claim 16, further comprising a galvanometer canner configured to move a beam emitted by the laser across the powder bed.
 19. The apparatus for forming cutting blades according to claim 16, further comprising a powder dispenser configured to spread a layer of powder across the powder bed.
 20. The apparatus for forming cutting blades according to claim 16, further comprising a processor programmed with a plurality of profiles for scanning the laser over the powder bed to form two-dimensional and three-dimensional shapes of a cutting edge of the cutting blade. 